90 INTRODUCTION. 



covering only one side of the end of a digit, leaving 

 the other completely bare for the functions of tact. 



The kind of food is manifested hy the form of the 

 molar teeth, which always indicate the same kind of 

 action as the articulation of their jaws. For cutting 

 flesh, the molars are always serrated, or toothed like 

 a saw, and the jaws are hung close, so that they only 

 open and shut like shears. The molar teeth, des- 

 tined for bruising grain and roots, have flat crowns, 

 and the jaws have a power of motion in an horizon- 

 tal direction, that is, of grinding; and, in order to 

 produce the same ridgy property which we give to 

 millstones, the crown of the molars is composed of 

 two different substances, the one harder than the 

 other, and, therefore, unequal in wearing down. 



The ungulate quadrupeds are necessarily all her- 

 bivorous, or with flat-crowned molars, because their 

 feet are not constructed to seize a living prey. 



Animals with unguiculated feet, being susceptible 

 of more variety, offer greater differences in the form 

 of their molars, and in the mobility and sensibility 

 of their digits : there is, moreover, a characteristic 

 which affords immense sway over their dexterity 

 and mode of action; it is the faculty of opposing 

 the thumb to the other fingers, so as to seize the 

 smallest objects, which constitutes a hand properly 

 so called. This power is carried to the highest per- 

 fection in man, who possesses the whole anterior 

 extremity free, and can employ it exclusively for 

 prehension. 



After the order which is solely occupied by man, 



